@brenty Sorry for the delay, needed to access the machine showing the problem to test properly and I've been travelling for a few days. Your questions and my answers:
Q: Do you have multiple Login items with the URL for that website saved in 1Password?
A: Nope, there is only one login item with this URL, as far as I know. If you can let me know a way of determining that for sure, I can test. But definitely, if I type the www.tld of the URL into the 1Password search, only one item is returned.
Q: And, if so, and they're not showing up when you open 1Password there in your browser, do you maybe have some in hidden vaults, or have "Display" set to "Never suggest in browser" set for them when editing?
A: No hidden Vaults as far as I can tell. Item that should be filled is in my personal Vault, and other websites are populated with information from this vault without problem. "Display" is set to "Suggest in browser" for this particular Login item,
As for seeing the item, the Suggested item does not appear on the left as you put it. See screenshot. The only items I see in the left pane, other than the "suggestions" button (the item with the up/down chevrons next to it) are my credit card items. The actual suggested item does not appear anywhere in the left hand pane of the window. Clicking the "suggestions" text (the one with the chevrons) takes me to a drop down with all the vault Categories, but no obvious entry to select the item that 1Password clearly has determined has a match. Hence, I can't select it to see the details, nor can I select the "Auto Fill" button to fill the details into the web form.
I don't understand that dropdown - what should it be displaying?
Could you please post a screenshot of the Login item you want 1Password to fill on this page, blanking out your credentials? I'm especially curious to see what the contents of the website field(s) is, if anything.
@Ben Hi, the website field matches exactly the one in the URL displayed in Safari.
Well... admittedly, that is really odd. I just tried saving a Login item for that site and like you've described it does not show up as a suggested item for me. I'm going to file an issue with our team to look into the root cause of that. I'm sorry for the inconvenience.
@Ben Not a problem - glad I wasn't doing something stupid there. Do let me know if you need anything else tested.